There is known a standard named DVB-C which was established in 1994 as a cable television broadcasting standard and is mainly adopted in Europe, while a standard named DVB-C2 has been proposed as a next-generation cable television broadcasting standard which replaces the DVB-C (refer to Non-Patent Document 1, for example).
The DVB-C2 is adapted to be able to provide a band (hereinafter referred to as a notch) in which a transmission signal is not transmitted even when the band is within a frequency band provided for CATV, so that a transmission signal of the CATV does not mutually interfere with a transmission signal used for a different purpose (such as radio communication provided for the police or radio communication provided for the military).
Now, an existing broadcasting system is adapted to investigate in advance a frequency band of a transmission signal that is used for a different purpose and can interfere with a transmission signal used for the CATV, and provide a notch corresponding to the frequency band.